The aim of this study was to determine the effect of the induced stress and restraint provided by the underlying bone on the frequency-dependent storage and loss stiffness (for bone restraint) or modulus (for induced stress) of articular cartilage, which characterise its viscoelasticity. Dynamic mechanical analysis has been used to determine the frequency-dependent viscoelastic properties of bovine femoral and humeral head articular cartilage. A sinusoidal load was applied to the specimens and out-of-phase displacement response was measured to determine the phase angle, the storage and loss stiffness or modulus. As induced stress increased, the storage modulus significantly increased (p < 0.05). The phase angle decreased significantly (p < 0.05) as the induced stress increased; reducing from 13.1° to 3.5°. The median storage stiffness ranged from 548N/mm to 707N/mm for cartilage tested on-bone and 544N/mm to 732N/mm for cartilage tested off-bone. On-bone articular cartilage loss stiffness was frequency independent (p > 0.05); however, off-bone, articular cartilage loss stiffness demonstrated a logarithmic frequency-dependency (p < 0.05). In conclusion, the frequency-dependent trends of storage and loss moduli of articular cartilage are dependent on the induced stress, while the restraint provided by the underlying bone removes the frequency-dependency of the loss stiffness.

Glaucoma is a major cause of irreversible blindness worldwide. The most acknowledged biomarker to diagnose and monitor glaucoma progression is intraocular pressure (IOP). Gold standard techniques for IOP monitoring are invasive, uncomfortable, and require visiting a clinic. In addition, most methods only provide a single snapshot on widely varying parameters. On the other hand, contact lenses have attracted particular interest to be used as continuous monitoring platforms to incorporate sensors, drugs, and more. Here, commercial contact lenses were laser-processed to be capable of detecting IOP variations in the physiological range. Three ring-couples with interspaces of 1.0, 1.5, and 2.0 mm were engraved on three soft contact lenses separately by using a carbon dioxide laser. The IOP/pressure variations induced repeatable changes in the ring-couple interspace which acted as a smartphone-readable pressure sensor. The processed contact lenses may be a potential candidate toward IOP monitoring at point-of-care settings.